A NOVEL TYPE OF PATHOGEN DEFENSE-RELATED CINNAMYL ALCOHOL-DEHYDROGENASE

We describe an aromatic alcohol dehydrogenase with properties indicati ng a novel type of function in the defense response of plants to patho gens, To obtain the enzyme free of contamination with possible isoform s, a parsley (Petroselinum crispum) cDNA comprising the entire coding region of the elicitor-responsive gene, ELl3, was expressed in Escheri chia coli, In accord with large amino acid sequence similarities with established cinnamyl and benzyl alcohol dehydrogenases from other plan ts, the enzyme efficiently reduced various cinnamyl and benzyl aldehyd es using NADPH as a cc-substrate, Highest substrate affinities were ob served for cinnamaldehyde, 4-coumaraldehyde and coniferaldehyde, where as sinapaldehyde, one of the most efficient substrates of several prev iously analyzed cinnamyl alcohol dehydrogenases and a characteristic p recursor molecule of angiosperm lignin, was not converted, A single fo rm of ELl3 mRNA was strongly and rapidly induced in fungal elicitor-tr eated parsley cells, These results, together with earlier findings tha t the ELl3 gene is strongly activated both in elicitor-treated parsley cells and at fungal infection sites in parsley leaves, but not in lig nifying tissue, suggest a specific role of this enzyme in pathogen def ense-related phenylpropanoid metabolism.